Transformer protective device



2 Sheets-Sheet 1 Filed July 20, 1955 oufo mm om wm\ NN w 2 by Q i g I 9 mm m mm on 3 mm m o mm on t Dec. 20, 1955 s. RADKoWsKl 2,727,613

TRANSFORMER PROTECTIVE DEVICE Filed July 20, 1953 2 Sheets-Sheet 2 Fig.2.

WITNESSES: INVENTOR J44 KM wf 7%745' United States Patent Ofitice 2,72 7,613 Patented Dec. 20, 1955 TRANSFQRMER PRUTE C'MVE DEVICE Leo S. Radkowski, Sharon, Pm, assignor to Viestinghcuse Electric Corporation, East Pittsburgh, 1%., a. corporation of Pennsylvania Application .lnly 26, 1953, Serial No. 369,1d4

6 Claims. Il. 192*133) This invention relates to transformers and more particularly to protective means associated therewith.

The output voltage of transformers is oftentimes varied by means of a tap-changer associated therewith. When a tap-changer is used, it must be capable of eifecting a change in the output voltage of the transformer without interrupting the input or output circuits of the transformer. In order to accomplish this operation under load, it is necessary to provide at least two movable contact members so that one of the movable contact mem here will at all times maintain an uninterrupted electrical circuit from the input to the output or" the transformer. However, when the movable contact members are in engagement with different stationary contact members, the current flow through these movable contact members would be excessive unless a preventive autotransformer were connected thereto.

When the tap-changer is rotated beyond its minimum or maximum position, the preventive autotransformer is connected across all the tapped portion of the transformer winding thus causing excessive current to flow through the preventive autotransformer. In most transformers having a tap-changer associated therewith, a stop mechanism is provided to prevent the actuation of the tap-changer beyond the minimum and maximum positions. However, heretofore such stop mechanisms occupied a considerable amount of space thus increasing the overall size of the apparatus. In those cases where space is limited it is extremely important to keep the size of the overall apparatus to a minimum.

An object or" this invention is to provide for preventing damage to a transformer having a tap-changer associated therewith, by so interconnecting a novel mechanical stop mechanism with the tap-changer that the actuation of the tap-changer beyond a minimum and maximum position is prevented.

Another object of this invention is to provide a transformer tap-changer stop mechanism which occupies a minimum of space, by so disposing the prongs of a pivoted forked member astridc a stop disk that the prongs of the forked member and the stop disk cooperates to prevent the actuation of the tap-changer beyond a minimum and a maximum position.

A further object of this invention is to provide for increasing the life of transformer tap-changer stop mechanism, by providing a breaking or decelerating elfect before the stop mechanism abruptly prevents a further positioning of the tap-changer in a given direction.

Other objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawings in which:

Figure l is a schematic diagram of apparatus and circuits illustrating the teachings of this invention;

Fig. 2 is a sectional view of the apparatus illustrated in Fig. l taken along the line llll, and

Fig. 3 is a sectional view of the apparatus illustrated in Fig. 1 taken along the line LIL-ill.

Referring to Fig. 1, there is illustrated an autotransformer 10 having a fixed winding 12 and a tapped winding 14 which receive energy from the supply terminals 15 and 15 and supply energy to the load terminals 16 and 16. In order to vary the amount of the tapped Winding 14 that is connected in circuit relationship with the fixed winding 12, a tap-changer 17 is electrically connected to the tapped winding 14 and to the fixed Winding 12 of the autotransformer ill. However, in order to prevent the tap-changer 17 from being actuated beyond the minimum and maximum limits of its operating range thereby causing damage to the tap-changer 17, a mechanical stop mechanism 18 is provided.

Referring more particularly to Fig. 1, it is to be noted that the tap-changer 17 includes two movable contact members 22 and 24 which are actuated by either a reversible motor 26 or by a hand crank 28 through suitable mechanical linkages which will be described hereinafter. in practice, the motor 26 is controlled in response to the output voltage of the autotransformer 10 to thereby effect an actuation of the tap-changer 17 in such a direction to automatically regulate the output voltage of the autotransformer it Limit switches (not shown) Well known in the art are also provided in order to deenergize the motor 26 once the tap-changer 17 has been actuated to either of its extreme positions. However, in accordance with the teachings of this invention the tap-changer i7 is prevented from being actuated by the hand crank 28 beyond the maximum and minimum limits of its operating range by the mechanical stop mechanism 18. Of course, before actuating the tap-changer 17 by means of the hand crank 28 the motor as is deenergized.

As can be seen from Fig. 1 of the drawings, one end of the movable contact member 22 remains in electrical contact with a conducting ring 39 when the contact member 22 is being actuated into its various positions around the ring 36 by means of either the motor 26 or the hand crank 2-8. As the movable contact member 22 is being actuated through its various positions, the other end of the contact member 22 engages a plurality of stationary contact members 34-, 35, 38, 4t 42, 44, 46, iii and 5b, which are electrically connected to the tapped winding 14 of the autotransformer 10. In like manner, one end of the movable contact member 24 selectively engages these stationary contact members 34, 36, 38, 40, 42, 44, 46, 48 and 5b, as it is actuated through its various positions. However, the other end of the movable contact member 24 during these various positions remains continuously in electrical contact with a conducting ring 52.

In order to connect the tapped winding 14 so that its turns either aid or buck the turns of the fixed winding 12 a reversing switch 54 is provided. In this instance, the reversing switch 54 comprises two stationary contact members 56 and 58 which are selectively engaged by a movable contact member 60 which is mechanically connected to a gearing mechanism 61 as will be explained more fully hereinafter. As illustrated, the stationary contact 56 is electrically connected to one end of the tapped winding 14, and the stationary contact member 58 is electrically connected to the other end of the tapped Winding 14.

For the purpose of interconnecting the fixed winding 12 with the tapped winding 14, one end of the fixed winding 12 is electrically connected to the movable contact member 60 of the reversing switch 54. As can be seen from Fig. l the load terminal R6 is also electrically connected to the movable contact member so as well as to the stationary contact member 50 of the tap-changer 17. As illustrated, a preventive autotransformer 62 is electrically connected to the conducting rings 30 and 52, through conductors 66 and 68, respectively, in order to prevent excessive current flow through the bridged portion of the tapped winding 14 and in order to prevent excessive arcing at the movable contacts 22 and 24. The sequence of operation of the movable contact members 22 and 24 of the tap-changer 17, as they move through the various tap-changing positions will be described here inafter.

In accordance with the teachings of this invention, the mechanical stop mechanism 18 is provided in order to insure that the tap-changer 17 can not be actuated beyond its extreme positions of minimum and maximum output for the autotransformer 10, which action would cause damage to the preventive autotransformer 62 since it would then become connected across all of the tapped winding 14. As illustrated, the mechanical stop mechanism 18 comprises a stop disk 70 having a spiral cam 72 disposed on one side thereof and a spiral cam 74 disposed on the other side thereof. in practice, the spiral cams 72 and 74 can either be an integral part of the stop disk 70 such as a single casting comprising the stop disk 70 and the spiral cams 72 and 74, or the spiral cams 72 and 74 can be suitably secured to the stop disk 70 by, for instance, welding. The spiral cams 72 and 74 incline inwardly towards their respective associated side of the stop disk 70, the spiral cam 72 functioning as a stop member when the stop disk 70 rotates in one direction and the spiral cam 74 functioning as a stop member when the stop disk 70 is rotated in the opposite direction. In particular, one end of the spiral cam 72 has an inclined stop surface 80 that makes an acute angle with the associated side of the stop disk 70. On the other hand, one end of the spiral cam 74 has an inclined stop surface 82 that makes an acute angle with its associated side of the stop disk 70. As will be explained more fully hereinafter the inclined stop surfaces 80 and 82 engage a pivoted fork member 84 to thereby prevent an actuation of the tap-changer 17 beyond its minimum and maximum positions.

As can be seen from Fig. l, the shaft 88 of the motor 26 extends through a shaft bearing 90 to receive the hand crank 28. A gear 92 is disposed on the other end of the shaft 88 of the motor 26, the gear 92 meshing with the gear teeth 94 of the stop disk 70. Thus, when the hand crank 28 is rotated in a clockwise direction the stop disk 70 rotates in a counterclockwise direction and when the hand crank 28 is rotated in a counterclockwise direction the stop disk 70 rotates in a clockwise direction.

In order that the stop disk 70 rotates in accordance with the positioning of the tap-changer 17, the stop disk 70 is mechanically connected to the movable contact members 22 and 24 of the tap-changer 17 through the gearing 61 and a mechanical connection 98. It is to be noted that the gear ratio of the gearing 61 is such that only a small fraction of the rotary force appearing at the output shaft 100 of the gearing 61 appears at the stop disk 70. Therefore, with the stop disk 70 so positioned, the mechanical strength and thus the size of the stop disk 70 need not be as great as compared to the case where a stop disk (not shown) were disposed on the output shaft 100 of the gearing 61.

Referring more particularly to the pivoted fork member 84, the member 84 is pivoted about a shaft 101 and comprises two prongs 102 and 104 and an extension 105. As illustrated, the prong 102 is disposed to be actuated into engagement with the spiral cam 72 when the tapchanger 17 approaches its minimum position so as to produce a minimum output voltage from the autotransformer 10. On the other hand, the prong 104 of the pivoted fork member 84 is disposed to be actuated into engagement with the spiral cam 74 when the tap-changer 17 approaches its maximum position in which a maximum output voltage is obtained from the autotransformer 10.

In order to pivot the fork member 84 in one direction once the tap changer 17 approaches its minimum position so that the prong 102 engages the spiral cam 72 and so that the forked member 84 is pivoted in the opposite direction once the tap-changer 17 approaches its maximum position so that the prong 104 engages the spiral cam 74, an actuating member 106 is provided. However, in order that the actuating member 106 moves or rotates in accordance with the positioning of the tapchanger 17, the actuating member 106 is mechanically connected to the output shaft of the gearing 61 through gear members 110 and is mechanically connected to the movable contact members 22 and 24 of the tapchanger 17 through the gear members 110 and the mechanical connection 98.

For the purpose of centering the pivoted forked member 84 with respect to the stop disk 70 when the tapchanger 17 is actuated from either its minimum or max imum limit to an intermediate position and to continue to center the fork member 64 with respect to the stop disk 78 when the tap-changer 17 is in its intermediate positions, a centering device 114 is provided. In other words, the centering device 114 biases the pivoted forked member to a predetermined position with respect to the stop disk 70 when the tap-changer 17 is in its intermediate positions. As illustrated, the centering device 114 comprises a compression spring 116 which is dis posed around a shaft 118. A freely rotatable wheel 120 is disposed on one end of the shaft 118, the wheel 120 being disposed adjacent the center line 122 of the shaft 101. In particular, the wheel 120 is biased against a V-shaped member 126, which comprises a part of the forked member 84, by means of the compression spring 116 which is disposed between a washer and a support member 132. In operation, the spring 116 exerts a force on the washer 130 which force is transmitted to the wheel 120.

The operation of the apparatus illustrated in the drawings will now be described. The output voltage of the autotransformer 10 as it appears across the load terminals 16 and 16 is at a minimum when the movable contact members 22 and 24 of the tap-changer 17 are both in electrical contact with the stationary contact member 48, and the movable contact member 60 of the reversing switch 54 is in electrical contact with the stationary contact member 58. In order to increase the output voltage of the transformer 10, the hand crank 28 is rotated in a clockwise direction to thereby actuate the movable contact member 22 to such a position that it engages the stationary contact member 46. The output voltage of the autotransformer 10 is further increased by rotating the hand crank further in a clockwise direction to thereby actuate the movable contact member 24 so that it too makes electrical contact with the stationary contact member 46. This sequence of positioning of the movable contact members 22 and 24 is continued by rotating the hand crank 28 in a clockwise direction until both the movable contact members 22 and 24 are in electrical contact with the stationary contact member 34 of the tap-changer 17. Up to this position, the turns of the tap winding 14 buck the turns of the fixed winding 12. Then the hand crank 23 is rotated further in a clockwise direction until the movable contact member 22 makes electrical contact with the stationary contact member 50. The hand crank 28 is then further rotated in a clockwise direction to actuate the movable contact member 24 so that it will make electrical contact with the stationary contact member 50; however, as soon as the movable contact member 24 breaks contact with the stationary contact member 34, the movable contact member 60 of the reversing switch 54 is actuated so as to make electrical contact with the stationary contact member 56.

With both the movable contact members 22 and 24 in electrical contact with the stationary contactmember 50 and the movable contact member 60 of the reversing switch 54 in electrical contact with the stationary contact member 56 the tap-changer 17 is in the neutral position in which the input and output voltages of the autotransformer are substantially equal. By rotating the hand crank 28 further in the clockwise direction, the output voltage of the autotransformer 10 is further increased since the turns of the tapped winding 14 are now boosting the turns of the fixed winding 12. The output voltage of the autotransformer 10 continues to increase as long as the hand crank 28 is further rotated in a clockwise direction until finally both the movable contact members 22 and 24 of the tap-changer 17 engage the stationary contact member 34. However, just before this position of the movable contact members 22 and 24 is reached, the actuating member 106 engages, as shown in the drawings, the extension 105' of the fork member 84 to thereby pivot the fork member 84 about the shaft 101 until the prong 104 of the fork member 84 engages the cam surface 140 of the spiral cam 74 at a position just beyond the stop surface 82 of the cam 74. On actuating the hand crank 28 further in the clockwise direction the actuating member 106 rotates further to thereby cause the end of the prong 104 to slide along the cam surface 140 of the spiral cam 74 until the end of the prong 104 engages the stop surface 82 of the spiral cam 74. When the prong 104 engages the stop surface 82 further positioning of the tap-changer 17 in the same direction is prevented.

On rotating the hand crank 28 in a counterclockwise direction to return the tap-changer 17 to its normal operating range, the centering device 114 effects a centering of the fork member 84 with respect to the stop disk 70 since the wheel 120 will always try to center itself in the middle of the V-shaped member 126. In order to return the output voltage of the autotransformer 10 to its minimum value the hand crank 28 is rotated further in a counterclockwise direction until both the movable contact members 22 and 24 are in electrical contact with the stationary contact member 48 of the tap-changer 17 and the movable contact member 60 of the reversing switch 54 is in electrical contact with the stationary contact member 58. However, just before the movable contact member 22 engages the stationary contact member 48 of the tap-changer 17, the actuating member 106 engages the extension 105 of the fork member 84 to thereby pivot the fork member 84 in such a direction as to bring the prong 102 into engagement with the cam surface 142 of the spiral cam 72 at a position just beyond the stop surface 80 of the spiral cam 72. Further rotation of the hand crank 28 in a counterclockwise direction effects a further rotation of the actuating member 106 in the same direction to thereby cause the end of the prong 102 to slide along the cam surface 142 of the spiral cam 72 until the end of the prong 102 engages the stop surface 80 of the spiral cam 72. When the end of the prong 102 engages the stop surface 80 further rotation of the hand crank 28 in a counterclockwise direction is prevented and further positioning of the tap-changer 17 in the same direction is likewise prevented. On rotating the hand crank 28 in a clockwise direction to return the tap-changer 17 to its normal operating range, the centering device 114 again effects a centering of the forked member 84 with respect to the stop disk 70.

It is to be noted that the stop surface 80 of the spiral cam 72 is inclined to such a degree that when the end of the prong 102 of the fork member 84 engages the stop surface 80 the spiral cam 72 exerts a force that passes to the right of the center line 122 of the shaft 101, as illustrated, to thereby effect a locking action between the end of the prong 102 and the stop surface 80 and thus prevent the end of the prong 102 from bouncing to the left, as illustrated in Fig. 1, once it e11- gages the stop surface 80. The stop surface 82 of the spiral cam 74 is likewise inclined to such a degree that the force exerted by the spiral cam 74 passes to the left of the center line 122 of the shaft 101, as illustrated. Such being the case, the end of the prong 104 likewise looks itself with respect to the stop surface 82 of the spiral cam 74 once the end of the prong 104 engages the stop surface 82.

By providing the spiral cam 72 so that the end of the prong 102 slides along the cam surface 142 of the spiral cam 72 and by providing the spiral cam 74 so that the end of the prong 104 slides along the cam surface 140 of the spiral cam 74, a breaking or de celerating effect is provided before the ends of the prongs 102 and 104 engage their respective stop surfaces and 82. Thus, the ends of the prongs 102 and 104 are prevented from abruptly engaging their respective associated stop surfaces 80 and 82. This sliding action of the ends of the prongs 102 and 104 along the cam surfaces 142 and 140, respectively, also gives an indication to the person actuating the hand crank 28 that one or the other of the extreme positions of the tap-changer 17 is near at hand since the hand crank 28 will become harder to turn.

Since certain changes may be made in the above apparatus and circuits, and dilferent embodiments of the invention may be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In a mechanical stop mechanism for limiting the positioning of a tap-changer that is disposed to vary the output voltage of a transformer, the combination comprising, a stop disk having a stop member disposed on each side thereof, means for rotating the stop disk in accordance with the positioning of the tap-changer, a pivoted forked member having two prongs disposed astride the stop disk, one of said prongs being disposed to be actuated into engagement with the stop member disposed on one side of the stop disk and the other of said prongs being disposed to be actuated into engagement with the stop member disposed on the other side of the stop disk, an actuating member disposed to move in accordance with the positioning of the tap-changer so as to actuate said one of said prongs into engagement with its associated stop member when the tap-changer reaches a predetermined position in one direction and so as to actuate said other of said prongs into engage ment with its associated stop member when the tapchanger reaches a predetermined position in the opposite direction, and means disposed to bias the pivoted forked member to a predetermined position with respect to the stop disk when the tap-changer is in its intermediate positions.

2. In a mechanical stop mechanism for preventing the actuation of a tap-changer, that is disposed to vary the output voltage of a transformer, beyond the minimum and maximum limits of its operating range, the combination comprising, a stop disk having a stop member disposed on each side thereof, means for rotating the stop disk in accordance with the positioning of the tap-changer, a pivoted fork member having two prongs disposed astride the stop disk, one of said prongs being disposed to be actuated into engagement with the stop member disposed on one side of the stop disk and the other of said prongs being disposed to be actuated into engagement with the stop member disposed on the other side of the stop disk, an actuating member disposed to move in accordance with the positioning of the tapchanger so as to actuate said one of said prongs into engagement with its associated stop member when the tap-changer reaches a predetermined position in one direction and so as to actuate said other of said prongs into engagement with its associated stop member when the tap-changer reaches a predetermined position in the opposite direction, and a centering device disposed to engage the pivoted fork member so as to center the pivoted fork member with respect to the stop disk when the tap-changer is actuated from its minimum and maximum limits to an intermediate position.

3. In a mechanical stop mechanism for limiting the positioning of a tap-changer that is disposed to vary the output voltage of a transformer, the combination comprising, a stop disk having a spiral cam disposed on each side thereof, one end of each of the spiral cams having a stop surface and each of the spiral cams having a cam surface, means for rotating the stop disk in accordance with the positioning of the tap-changer, a pivoted fork member having two prongs disposed astride the stop disk, one of said prongs being disposed to be actuated into engagement with the cam surface of the spiral cam disposed one one side of the stop disk and the other of said prongs being disposed to be actuated into engagement with the cam surface of the spiral cam disposed on the other side of the stop disk, an actuating member disposed to move in accordance with the positioning of the tap-changer to thereby engage the pivoted fork member and actuate said one of said prongs into engagement with the cam surface of its associated spiral cam so that said one of said prongs slides along the cam surface of its associated spiral cam until it engages the stop surface of its associated spiral cam thus preventing further positioning of the tap-changer in one direction and to thereby engage the pivoted fork member and actuate said other of said prongs into engagement with the cam surface of its associated spiral cam so that said other of said prongs slides along the cam surface of its associated spiral cam until it engages the stop surface of its associated spiral cam thus preventing further positioning of the tap-changer in the opposite direction.

4. In a mechanical stop mechanism for preventing the actuation of a tap-changer, that is disposed to vary the output voltage of a transformer, beyond the minimum and maximum limits of its operating range, the combination comprising, a stop disk having a spiral cam disposed on each side thereof, one end of each of the spiral cams having a stop surface and each of the spiral cams having a cam surface, means for rotating the stop disk in accordance with the positioning of the tap-changer, a pivoted fork member having two prongs disposed astride the stop disk, one of said prongs being disposed to be actuated into engagement with the cam surface of the spiral cam disposed on one side of the stop disk and the other of said prongs being disposed to be actuated into engagement with the cam surface of the spiral cam disposed on the other side of the stop disk, an actuating member disposed to move in accordance with the positioning of the tap-changer to thereby engage the pivoted fork member and actuate said one of said prongs into engagement with the cam surface of its associated spiral cam so that said one of said prongs slides along the cam surface of its associated spiral cam until it engages the stop surface of its associated spiral cam thus preventing further positioning of the tap-changer in one direction and to thereby engage the pivoted fork member and actuate said other of said prongs into engagement with the cam surface of its associated spiral cam so that said other of said prongs slides along the cam surface of its associated spiral cam until it engages the stop surface of its associated spiral cam thus preventing further positioning of the tap-changer in the opposite direction, and a centering device disposed to engage the pivoted fork member so as to center the pivoted fork member with respect to the stop disk when the tapchanger is actuated from its minimum and maximum limits to an intermediate position,

5. In a mechanical stop mechanism for limiting the positioning of a tap-changer that is disposed to vary the output voltage of a transformer, the combination comprising, a stop disk having a spiral cam disposed on each side thereof, one end of each of the spiral cams having an inclined stop surface that makes an acute angle with its associated side of the stop disk and each of the spiral cams having a cam surface, means for rotating the stop disk in accordance with the positioning of the tapchanger, a pivoted fork member having two prongs disposed astride the stop disk, one of said prongs being disposed to be actuated into engagement with the cam surface of the spiral cam disposed on one side of the stop disk and the other of said prongs being disposed to be actuated into engagement with the cam surface of the spiral cam disposed on the other side of the stop disk, an actuating member disposed to move in accordance with the positioning of the tap-changer to thereby engage the pivoted fork member and actuate said one of said prongs into engagement with the cam surface of its associated spiral cam so that said one of said prongs slides along the cam surface of its associated spiral cam until it engages the inclined stop surface of its associated spiral cam thus preventing further positioning of the tap-changer in one direction and to thereby engage the pivoted fork member and actuate said other of said prongs into engagement with the cam surface of its associated spiral cam so that said other of said prongs slides along the cam surface of its associated spiral cam until it engages the inclined stop surface of its associated spiral cam thus preventing further positioning of the tap-changer in the opposite direction.

6. In a mechanical stop mechanism for preventing the actuation of a tap-changer, that is disposed to vary the output voltage of a transformer, beyond the minimum and maximum limits of its operating range, the combination comprising, a stop disk having a spiral cam disposed on each side thereof, one end of each of the spiral cams having an inclined stop surface that makes an acute angle with its associated side of the stop disk and each of the spiral cams having a cam surface, means for rotating the stop disk in accordance with the positioning of the tap-changer, a pivoted fork member having two prongs disposed astride the stop disk, one of said prongs being disposed to be actuated into engagement with the cam surface of the spiral cam disposed on one side of the stop disk and the other of said prongs being disposed to be actuated into engagement with the cam surface of the spiral cam disposed on the other side of the stop disk, an actuating member disposed to move in accordance with the positioning of the tap-changer to thereby engage the pivoted fork member and actuate said one of said prongs into engagement with the cam surface of its associated spiral cam so that said one of said prongs slides along the cam surface of its associated spiral cam until it engages the inclined stop surface of its associated spiral cam thus preventing further positioning of the tap-changer in one direction and to thereby engage the pivoted fork member and actuate said other of said prongs into engagement with the cam surface of its associated spiral cam so that said other of said prongs slides along the cam surface of its associated spiral cam until it engages the inclined stop surface of its associated spiral cam thus preventing further positioning of the tap-changer in the opposite direction, and a centering device disposed to engage the pivoted fork member so as to center the pivoted fork member with respect to the stop disk when the tap-changer is actuated from its minimum and maximum limits to an intermediate position.

References Cited in the file of this patent UNITED STATES PATENTS 2,479,555 Burbage Aug. 23, 1949 

